The goal of this project is to characterize the transposon-silencing pathway, specifically focusing on the endogenous role of small RNAs. Since the late 1980's, transposons have been well characterized in C. elegans through the use of classical genetic tools to interrogate questions related to mechanisms of transposition. In 1999, it was discovered that endogenous small RNA pathways regulate transposons and several screens were performed to isolate mutants with active transposition in the germline. However, although many mutants have been isolated in genes attributed to this pathway, little work has been done to mechanistically characterize the roles of individual proteins. Additionally, because most analyses of transposon movement were done prior to the advent of high-throughput sequencing, there is no genome-wide data examining transposon mobilization. In addition to transposons, many other types of transcripts are processed through the endogenous RNA pathways, including aberrant transcripts, duplicated and hypothetical genes, and non-coding regions, however the mechanism by which these transcripts are recognized and routed into these pathways is completely unknown. By probing the individual components of these pathways, examining what species of RNA they associate with, and to what process their enzymatic functions contribute, this project will achieve a more complete understanding of transposon silencing. The proposed experiments herein aim to identify factors that regulate transposon mobilization, including genomic features, host proteins, and environmental stimuli with the goal of elucidating the mechanisms of action of the known and novel components of this pathway. The results of this work will have significant implications in understanding how active transposons affect gene expression and alter genome structure, which can result in many diseases including cancer. The Ruvkun lab is an ideal place to study regulation of transposons by RNAi machinery in C. elegans. The lab not only has extensive expertise in the small RNA field, but also in stress response pathways, high- throughput genetic screens, protein purification, and biochemistry. The laboratory environment contains an extremely motivated and scientifically diverse group of researchers interested in fundamental aspects of C. elegans biology. The lab is flanked by two excellent C. elegans labs studying neurobiology and pathogenesis and is supported by a highly collaborative department that houses labs with expertise in RNA biology and chromatin structure. I plan to utilize all of these resources during the rest of my post-doctoral tenure. Throughout my research career, I have been focused on chromatin and RNA biology, which are fundamentally important in the understanding and prevention of cancer. Specifically, greater understanding of RNA silencing and transposon quiescence may lead to advances in cancer diagnoses or therapeutics. I am committed to a career in academic research and plan to start a lab focused on the aims in this proposal.